The present invention relates generally to the machining of rotating workpieces and, in particular, to a cutting insert that may be used to perform grooving, turning, boring, face grooving, face turning and profiling operations.
Metal cutting inserts, particularly the so-called dogbone shaped varieties, which have capabilities of removing metal in both the radial and axial directions have been known to the art for several decades. This style of insert initially was ground all over and offered no topographical features to reduce cutting pressures or assist in chip control.
Cutting inserts of the type to which this invention is directed, have circular cutting edges and are generally employed in turning operations where the cutting portion of the insert is designed to machine a workpiece into a relatively complicated shape. In these types of operations, the cutting insert is positioned and moved by a slide mechanism with respect to the workpiece. The slide mechanism for some operations may move the insert in a continuously changing direction in order to achieve the desired shape in the workpiece.
The continuous changes in direction of movement in the cutting insert and the changing contact point between the workpiece and the circular cutting edge of the insert make chip control more difficult.
Although cutting inserts with circular edges are commercially available, it is believed that many of the existing designs do not adequately deal with chip control over the range of speeds, feeds, variable depths of cut and materials available. Inadequate chip control can adversely affect the life of the tool and can also damage the workpiece.
Chip control is important on cast workpieces where changing surface contours result in variable depths of cut to be achieved by a given tool acting in a multi-axial mode. Absence of chip control during this type of operation can be inconvenient and costly.
Enhancements to the early inserts of this type offered a variety of chip controlling devices which provided some degree of chip control in both the radial and axial directions. However, these enhancements to chip control did not function optimally over the varying depths of cut and changing contours of the workpieces, especially at very shallow depths of cut.
Later advancements in the art placed a greater amount of emphasis on achieving chip control at shallow depths of cut but did so at the expense of increased cutting pressures and with some reduction in surface finish quality. Even further, some of the chip control devices which purported to reduce cutting pressure and improve finish were restricted in size or shape such that they could not offer chip control over a complete range of depths of cut in all cutting modes.
The present invention provides a new and improved cutting insert that is capable of performing multiple machining operations, such as turning, profiling, grooving, etc. and which includes chip controlling and chip breaking surfaces which improve chip management during its use.
According to the invention, the metal cutting insert has a substantially circular cutting edge defined by the juncture of a clearance surface and a circular rake surface. A plurality of elongate, spaced apart radially directed recesses have outer ends that merge with the circular rake surface and inner ends that merge with a plateau-like surface that is formed generally centrally with respect to the circular cutting edge and which has an upper surface located at a level higher than the cutting edge. The plateau-like surface defines a discontinuous circular edge in the form of arcuate ridges. A plurality of chip deflectors defined in part by shallow depressions are located between associated recesses and extend from the rake surface and merge with an associated ridge formed by the plateau-like surface.
According to the preferred embodiment, the rake surface which extends inwardly with respect to the cutting edge is frusto-conical in shape and is angled downwardly to define a positive rake surface. According to this preferred embodiment, the cutting edge itself is located in a common plane which is preferably coplanar with the machine tool center line.
In a more preferred embodiment, the recesses have a longitudinal extent that is greater than the chip deflectors, such that the ridges defined by the plateau-like surface are disposed between associated recesses.
In the exemplary embodiment, each recess includes a base surface that extends downwardly from the rake surface and merges with an upwardly extending arcuate wall that defines, at least in part, the inner end of its associated recess. Preferably, the base surface of the recess is substantially below the level of an adjacent chip deflector. In the preferred embodiment, each recess is a substantially constant transverse dimension and the chip deflectors have a decreasing transverse dimension, such that an outer end of each deflector has a transverse dimension substantially greater than an inner end of the chip deflector.
The disclosed surface configurations provide chip control under various operating parameters. For shallow depths of cut, the positive rake surface serves to deflect the chip into a tight spiral and direct it toward a chip deflector. Impact with a chip deflector will then break the tightly spiraled chip. At greater depths of cut, portions of the recesses will impede the flow of at least portions of the chip and which, in conjunction with the positive rake surface, will serve to further tighten the chip spiral and cause it to break into a shorter length. At still greater depths of cut, additional recesses will come into play and act to rigidize the chip by inducing a portion of it to flow into the recess, creating a rib in the chip. The positive orientation of both the chip deflectors and recesses ensures that chip breaking will occur with a minimal increase in cutting pressure.
The radial orientation and uniform spacing of the chip deflectors and recesses in conjunction with the positive rake surface provide for similar performance irrespective of the orientation of the insert and contact point along the cutting edge. The symmetrical orientation of the chip controlling devices ensures the same chip control capabilities irrespective of the direction of movement of the tool.
According to a further feature of the invention, the metal cutting insert preferably includes metal cutting portions disposed on either side of a shank portion. In the preferred construction, when one of the cutting portions is worn, the tool is removed from its tool holder and rotated 180xc2x0 in order to position the opposite, unused cutting portion into a machining position. According to this feature, the cutting insert includes a protuberance that is centrally located with respect to the cutting portions and which is engageable by a clamp forming part of the cutting tool system and which secures the insert in a cutting position.
In the preferred construction, the insert is formed by a relatively hard material, such as carbide, cermet or ceramic. The insert may be molded using a powder metal technology that is known in the art. In the preferred embodiment, the insert is molded using known technology and is intended for single use. With the preferred construction, the cutting insert is disposed of after its cutting portions are worn and is not intended to be resharpened or remanufactured.